1. Field of the Invention
The invention relates to kidney dialyzers, and more specifically to hollow fiber dialyzers.
2. Description of the Related Art
Each year, a significant number of people worldwide develop kidney problems or kidney failure. A majority of these people require temporary or permanent help with the elimination of dissolved waste in the bloodstream. This elimination must be performed to prevent the development of such conditions as uremia and electrolytic imbalance. When these conditions develop and are left untreated, the bloodstream becomes increasingly toxic, and death can occur within days.
The standard medical treatment to eliminate bloodstream waste is hemodialysis (HD), also called simply dialysis. The hemodialysis machine is composed of two main components: the dialyzer or semipermeable membrane, and the pumps and monitors. Blood flows on one side of the membrane while a physiologic solution, called dialysate, flows on the opposite side. The actual process of hemodialysis occurs across the dialyzer membrane. This process involves the forces of diffusion, convection and ultrafiltration. During diffusion small molecules and toxins diffuse from the blood side of the membrane to the dialysate side to purify the blood. During convection the passage of small molecules and toxins are transported through the membrane. This transportation is caused by the hydrostatic pressure of the blood, even in the absence of dialysate on the other side of the membrane. During ultrafiltration the fluid under hydrostatic pressure from the blood side of the membrane moves to the dialysate side.
There have been many changes in the design and geometry of the dialyzer. These have included the designs of Kolff's rotating drum, Kiil's flat plate, Kolff's twin coil and the disposable flat plate. Dialysis membranes have also undergone significant development, advancing from sausage casing to today's biocompatible membranes. For the last 25 years, the hollow fiber membrane dialyzer, developed by the United States National Institutes of Health, has been the most commonly used design. Pairing this design with membranes possessing various characteristics has fostered the development of different modalities of therapy. These include regular hemodialysis (HD), high efficiency HD, high flux HD, hemofiltration, hemodiafiltration, ultrafiltration and plasmapheresis. While there have been significant changes in membrane materials since the development of the hollow fiber dialyzer, the geometry and design of the dialyzer have remained essentially the same.
The flow of fluids and solutes through a membrane during dialysis shows significantly less resistance when tested in vitro as compared to in vivo measurements using blood. This is partially because some of the proteins in the blood are adsorbed to the membrane surface. These adsorbed proteins form a layer over the dialyzer membrane which causes resistance, counteracting the forces of diffusion, convection and ultrafiltration. The higher the protein content of a solution being filtered, the lower the rate of these three forces are achieved. This is a major factor hindering the development of more efficient dialysis since the clearance of middle-sized molecules and other uremic toxins from blood was slowed.
Hemofiltration and hemodiafiltration are two modalities that are more efficient than hemodialysis in achieving blood purification in a given period of time. Recent clinical studies concluded that patients treated with these therapies fared better than those treated with hemodialysis. However, these modalities are not popular. This is because they are very expensive; they require large amounts of fluid, up to 45 liters, which must be replaced with every treatment. Also, they require the modification or replacement of currently used dialysis machines. This makes a change to these therapies prohibitively expensive to most providers of dialysis therapy.
The main difference between these two modalities and hemodialysis is that they are driven by convective and ultrafiltrative transport, while hemodialysis is driven by diffusive transport. In hemofiltration and hemodiafiltration, the hollow fiber dialyzer is used to achieve maximum ultrafiltration and convection forces. In hemodialysis, the same hollow fiber dialyzer is used to achieve maximum diffusion. The hollow fiber dialyzer in its current form cannot maximize all three forces simultaneously. A dialyzer that will provide for the maximum use of these three forces at the same time is the subject of this invention.
Devices designed for the separation and cleansing of blood have been addressed in the prior art. U.S. Pat. No. 5,284,470, granted to Alex T. Beltz, discloses a wearable, portable, lightweight artificial kidney. This device uses chemical treatment instead of dialysis to purify separated plasma. Also, this device is meant for continuous rather than periodic use. Finally, water removal is provided.
U.S. Pat. No. 3,579,441, granted to Clinton E. Brown, discloses a method of blood purification by ultrafiltration. In this invention, ultrafiltration rather than dialysis is used to perform plasma cleansing. Also, this device is designed for continuous use, not periodic application. Further, after filtration, make-up electrolytes are provided.
U.S. Pat. No. 4,289,623, granted to K. Lee, discloses a hollow fiber dialyzer which dialyzes the plasma-blood combination. No means of separation of plasma from blood cells and proteins is disclosed.
U.S. Pat. No. 5,069,788, granted to J. M. Radovich et al., discloses a multi-pass blood washing and plasma removal device and method. This device separates plasma from whole blood and provides for washing of the plasma-depleted component, but does not wash the plasma component. Also, this invention does not provide for recombination of the components.
U.S. Pat. No. 4,789,473, B. Mathieu et al., discloses a method for obtaining plasma or plasma water. This device uses filtration to remove plasma from whole blood. No provision for dialysis or other cleansing is disclosed. Also, the plasma is not returned to the cellular blood component.
U.S. Pat. No. 4,729,829, granted to R. Duggins, discloses a hollow fiber plasmapheresis module which separates plasma from blood. No method of cleansing or plasma return is disclosed.
U.S. Pat. No. 5,008,012, granted to Haguhara et al., discloses a compact plasma separator and apparatus which also separates plasma from blood. No means for cleansing or plasma return are disclosed.
Nothing in the prior art provides for or suggests an apparatus which separates whole blood, dialyzes each component separately, and then combines the components for return to the patient.